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Intellec 4 MOD 40 working!

I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a week ago. Both are in phenomenal condition. They were bought from surplus in the

Message 1 of 5
, Nov 12, 2012

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I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a week ago. Both are in phenomenal condition. They were bought from surplus in the early-to-mid 1980s and stored for the next 30 years, not ever even turned on within that time period.

They were originally going to go in a computer memory display, but they didn't quite fit in, nor was there quite enough room for them. Since that fell through, they came into my hands as someone who was willing to clean them up and get them working again.

I have only a couple of issues with the 4 MOD 40, which is the only one I've cleaned up and actually gotten working at this point. One LED (bit 0) on the address indicator flickers sometimes, and another LED (bit 9) is completely dead. I'm not sure if it's a resistor, LED, or driver yet, but I'll be doing some more debugging this weekend, probably.

For those with a good eye for this kind of stuff, you would be correct if you thought the RAM board was in the wrong slot. It has since been corrected. That was the only real issue I've had, and mostly my fault for not being able to interpret the schematic correctly. In my defense, when I got the computer, the RAM board was in the slot it was now. Again, though, one should never assume that the configuration a machine is currently in is the correct one.

I now realized that having the RUN switch in the Search Address Control area *on* will prevent me from having to load an address higher than one the program will ever reach. It's essentially inserting a breakpoint, from what I understand. I've still got a ways to go on fully understanding its limited front-panel capabilities, but hopefully I won't have to if I get a terminal connected to it. Of course, that wouldn't be any fun! :)

Does anyone have a simple design for a 20mA current loop to RS-232 converter they would share? The Intellec unfortunately only offered current loop, since that I guess was the "hip" thing at the time. After all, who wouldn't want to type in their software and get the printout at a blazing 110 baud? :)

Enjoy,

Kyle

s100doctor

... This is a fantastic find! I ve wanted a MOD 80 for a long time. I have some MOD 40 stuff. When time permits me, I ll chat with you about Intellec stuff.

>
> I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a week
> ago. Both are in phenomenal condition. They were bought from surplus in the
> early-to-mid 1980s and stored for the next 30 years, not ever even turned
> on within that time period.

This is a fantastic find! I've wanted a MOD 80 for a long time. I have some MOD 40 stuff. When time permits me, I'll chat with you about Intellec stuff. But I hope you make up some Web pages about these two computers to document them and your work.

> Does anyone have a simple design for a 20mA current loop to RS-232
> converter they would share? The Intellec unfortunately only offered current
> loop, since that I guess was the "hip" thing at the time. After all, who
> wouldn't want to type in their software and get the printout at a blazing
> 110 baud? :)

This is like saying "unfortunately cowboys only rode horses, after all, who wouldn't want to travel on an animal and ride at a blazing 15 miles per hour?". Teletypes in 1975 and earlier offered text output, keyboard input, and program storage and entry (paper tape). Terminals generally didn't have ANY mass storage, otherwise - that came later.

Here's some preserved information about another computer, made not too much after the MOd 80 was available:

You may have to adjust the components for +5/-5v or +12/-12v operation but you may well get away with +5/0v. Just be sure that a RS-232 negative level (transmit low) doesnt' forward bias that base-emitter junction on Q1 and fry the transistor with too much current. This calls for a little transistor theory...

Circuits like these, depend a little on the voltage of your current source. I don't know if the Intellec has a current loop supply, or what it expects, see the docs. But in general, it's typical to use optoisolators to keep nasty current loop voltages (and electrical noise from TTY's) away from your microcomputer.

Herb Johnson

Kyle Owen

I fully intend to start my own web page soon. I may even try hosting it myself. We ll see how long I can do that before Charter complains. I have so much I can

Message 3 of 5
, Nov 13, 2012

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I fully intend to start my own web page soon. I may even try hosting it myself. We'll see how long I can do that before Charter complains. I have so much I can put on a web page, and it's just a matter of doing it at this point.

I was purely joking about the teletype. Indeed, it was one of the few options available at the time, and a far cry from what you could do with the front panel on the 4 MOD 40. Even a couple of years later, the SWTPC 6800 still had a serial board that would fully support the 20mA current loop for teletypes.

Thanks for the link regarding the current loop to TTL converter. I have a bunch of 4N28s, so I suspect a couple of those, a MAX232, and tapping "5V" off the 5V line through a 220 ohm resistor (the high side of the input current loop on the Intellec) will be sufficient. Of course, I'll have to test it before I can say this will work for certain. I may be able to put a rather large capacitor on the Vcc line of the MAX232 to keep the voltage a bit higher during times of high load.

--- In midatlanticretro@yahoogroups.com, Kyle Owen <kylevowen@...> wrote:
>
> I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a week
> ago. Both are in phenomenal condition. They were bought from surplus in the
> early-to-mid 1980s and stored for the next 30 years, not ever even turned
> on within that time period.

This is a fantastic find! I've wanted a MOD 80 for a long time. I have some MOD 40 stuff. When time permits me, I'll chat with you about Intellec stuff. But I hope you make up some Web pages about these two computers to document them and your work.

> Does anyone have a simple design for a 20mA current loop to RS-232
> converter they would share? The Intellec unfortunately only offered current
> loop, since that I guess was the "hip" thing at the time. After all, who
> wouldn't want to type in their software and get the printout at a blazing
> 110 baud? :)

This is like saying "unfortunately cowboys only rode horses, after all, who wouldn't want to travel on an animal and ride at a blazing 15 miles per hour?". Teletypes in 1975 and earlier offered text output, keyboard input, and program storage and entry (paper tape). Terminals generally didn't have ANY mass storage, otherwise - that came later.

Here's some preserved information about another computer, made not too much after the MOd 80 was available:

You may have to adjust the components for +5/-5v or +12/-12v operation but you may well get away with +5/0v. Just be sure that a RS-232 negative level (transmit low) doesnt' forward bias that base-emitter junction on Q1 and fry the transistor with too much current. This calls for a little transistor theory...

Circuits like these, depend a little on the voltage of your current source. I don't know if the Intellec has a current loop supply, or what it expects, see the docs. But in general, it's typical to use optoisolators to keep nasty current loop voltages (and electrical noise from TTY's) away from your microcomputer.

Herb Johnson

Dave McGuire

... Beautiful! I covet the 4/40. If I can ever pry it out of your hands with some tasty trade action, do let me know. -Dave -- Dave McGuire, AK4HZ New

Message 4 of 5
, Nov 14, 2012

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On 11/13/2012 02:18 AM, Kyle Owen wrote:

> I was given two Intellecs, a 4 MOD 40 and an 8 MOD 80, a little over a
> week ago. Both are in phenomenal condition. They were bought from
> surplus in the early-to-mid 1980s and stored for the next 30 years, not
> ever even turned on within that time period.
>
> They were originally going to go in a computer memory display, but they
> didn't quite fit in, nor was there quite enough room for them. Since
> that fell through, they came into my hands as someone who was willing to
> clean them up and get them working again.
>
> I have only a couple of issues with the 4 MOD 40, which is the only one
> I've cleaned up and actually gotten working at this point. One LED (bit
> 0) on the address indicator flickers sometimes, and another LED (bit 9)
> is completely dead. I'm not sure if it's a resistor, LED, or driver yet,
> but I'll be doing some more debugging this weekend, probably.
>
> Anyways, here's the album: http://imgur.com/a/2s18f

Beautiful! I covet the 4/40. If I can ever pry it out of your hands
with some tasty trade action, do let me know.

-Dave

--
Dave McGuire, AK4HZ
New Kensington, PA

Evan Koblentz

... +1 for the club s museum.

Message 5 of 5
, Nov 14, 2012

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>> Beautiful! I covet the 4/40. If I can ever pry it out of your hands with some tasty trade action, do let me know.

+1 for the club's museum.

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